Dual edge-triggered explicit pulse generator circuit

ABSTRACT

A pulse generator system is disclosed. The system includes a plurality of buffers and at least two transmission gates. The inverters successively insert delays into an input signal having a series of pulses, each pulse having first and second edges. The transmission gates are operatively coupled to the inverters. The first transmission gate selectively passes the input signal. The second transmission gate selectively passes inverted signal of the input signal.

BACKGROUND

[0001] This invention relates to a dual edge-triggered circuit, and more particularly to an explicit pulse generator circuit.

[0002] Dual edge-triggered circuits latch data on both the rising and falling edges of the clock. This may halve the clock frequency for the same data throughput. Since the power dissipation may be proportional to the frequency of operation, the total used power may be reduced. Further, since a significant portion of the total power of the circuit may be consumed in the clock distribution network, it may be advantageous to employ chips that operate on both edges of the clock. Thus, replacing conventional single edge-triggered circuits with dual edge-triggered circuit may result in up to 50% power savings in the clock distribution. However, the circuits must be designed in an energy-efficient manner to provide meaningful reduction in the total power consumption.

[0003] Prior art designs on creating dual edge-triggered flip-flops have been provided by replicating the latch elements of a single edge-triggered flip-flop and multiplexing the outputs. For example, M. Afghahi and J. Yuan, in “Double Edge-Triggered D-Flip-Flops for High-Speed CMOS Circuits”, IEEE Journal of Solid-State Circuits, pages 1168-1170, Vol. 26, No. 8, August 1991, suggest reducing the power dissipation of a clock distribution circuit by using flip-flops triggered on both edges of the clock pulses instead of on only one edge. The dual edge-triggered flip-flop is created from two true single-phase clock elements and a NAND gate. A. Gago et. al., in “Reduced implementation of D-type DET Flip-Flops”, IEEE Journal of Solid-State Circuits, pages 400-402, Vol. 28, No. 3, March 1993, present a dual edge-triggered static master-slave flip-flop. The design duplicates a single edge-triggered flip-flop but shares the clock transistors that are common to both latches. These implementations suffer from a larger clock load at the same level of performance as a single edge-triggered flip-flop. Therefore, this may offset gain from the reduced clock frequency.

DESCRIPTION OF DRAWINGS

[0004] These and other features and advantages of the invention will become more apparent upon reading the following detailed description and upon reference to the accompanying drawings.

[0005]FIG. 1 shows an explicit-pulsed static flip-flop element according to an embodiment of the present disclosure.

[0006]FIG. 2 shows a timing diagram of the explicit pulse generator shown in FIG. 1.

[0007]FIG. 3 illustrates one embodiment of a dual edge-triggered explicit-pulsed static flip-flop element.

[0008]FIG. 4 shows a timing diagram of the explicit pulse generator shown in FIG. 3.

[0009]FIG. 5 shows a method for generating explicit pulse signals.

DETAILED DESCRIPTION

[0010] In recognition of the above-described difficulties with conventional dual edge-triggered circuits, the present disclosure describes an explicit pulse generator that provides a dual edge-triggered signal. The explicit pulse dual edge-triggered circuit provides advantages over a conventional dual edge-triggered circuit by allowing larger energy savings from fewer device count and reduced clock load.

[0011] An explicit-pulsed static flip-flop element 100 according to an embodiment is shown in FIG. 1. The flip-flop element 100 includes an explicit pulse generator 102 and a flip-flop portion 120. This element 100 is a single edge-triggered flip-flop.

[0012] In the illustrated embodiment, the rising edge on the “Clk” input 104 produces a falling clock pulse on the PMOS transistor 108 of the transmission gate 106. The “Clk” input 104 also produces a rising clock pulse on the NMOS transistor 110 of the transmission gate 106. The width of the clock pulse, produced at the output of the explicit pulse generator 102, may be set by the number and sizes of inverters 112. Thus, the clock pulse may be set to achieve a reasonable balance between the amount of time borrowing desired and the maximum hold time that may be tolerated. Although no pulse is generated on the falling edge of the incoming clock, power is dissipated in the pulse generator 102 as the inverters 112 switch.

[0013]FIG. 2 shows a timing diagram of the explicit pulse generator 102 shown in FIG. 1. The timing diagram shows that the rising edge 200 on the Clk input produces a falling clock pulse 202 on the PMOS transistor 108 (node P) and a rising clock pulse 204 on the NMOS transistor 110 (node N). The pulses 202, 204 are generated when the input node B of the NAND gate 114 is delayed with respect to the input node A by the inverters 112. The NAND gate 114 outputs a falling edge pulse at node P, in response to the rising edge of the Clk input, when the input nodes A and B are both logic high. Therefore, the pulse width 206 is set by the delay generated by the inverters 112. Accordingly, the rising edge clock pulse 204 at the NMOS transistor 110 and the falling edge clock pulse 202 at the PMOS transistor 108 of the transmission gate 106 clocks data input D 116 to output Q 118 of the flip-flop.

[0014] One embodiment of a dual edge-triggered explicit-pulsed static flip-flop element 300 is illustrated in FIG. 3. The dual edge-triggered element 300 includes an explicit pulse generator system 302. The element 300 also includes a flip-flop portion 304 having the same design as the flip-flop portion 120 of the single edge-triggered element 100 shown in FIG. 1.

[0015] The explicit pulse generator system 302 includes a transmission-gate XOR circuit involving two transmission gates 306, 308. The transmission-gate XOR circuit provides a clock pulse generated on both edges of the incoming clock 310.

[0016] Since the flip-flop portion 304 has not been modified, there is no performance penalty for the dual edge-triggered design as compared to the single edge-triggered version. Further, since no replication is necessary, the total area of the dual edge-triggered element 300 may be smaller than the conventional dual edge-triggered design.

[0017] In the illustrated embodiment of the explicit pulse generator system 302 shown in FIG. 3, there are three inverters 312 and two transmission gates 306, 308. Each of the transmission gates 306, 308 includes a PMOS transistor and an NMOS transistor connected in parallel. The transistors in the transmission gate are controlled by a pair of complementary signals driving the gates of the transistors. For example, the transmission gate 306 is controlled by delayed signals, at nodes C and D, feeding the gate terminals of the NMOS and PMOS transistors, respectively. The transmission gate 308 is controlled by delayed signals, at nodes D and C, feeding the gate terminals of the NMOS and PMOS transistors, respectively. Input signals to the transmission gates 306, 308 are supplied by the input signal at node A and the delayed signal at node B, respectively. The outputs of the transmission gates 306, 308 are tied together to form a wired-OR configuration at node 314.

[0018]FIG. 4 shows a timing diagram of the explicit pulse generator system 302 shown in FIG. 3. The delayed clock pulses at nodes A through D are shown below the input clock pulse (“Clk”). The transmission gate 306 passes the input clock to the output node P1, when the pulse at node C is at logic high and the pulse at node D is at logic low. The transmission gate 308 passes the delayed pulse at node B to the output node P2, when the pulse at node D is at logic high and the pulse at node C is at logic low. Therefore at node P1, a falling clock pulse (indicated by solid line) is generated at the falling edge of the input clock 310. At node P2, a falling clock pulse (indicated by solid line) is generated at the falling edge of the signal at node B. This signal may be a delayed rising edge of the input clock 310.

[0019] Accordingly, falling clock pulses are generated at both edges of the input clock at node P, as shown in FIG. 4. Rising clock pulses are generated at both edges of the input clock at node N.

[0020]FIG. 5 shows a method for generating explicit pulse signals. The method includes successively inserting a delay into an input signal, at 500. The input signal and delayed signals of the input signal are then coupled, at 502. At 504, the input signal is selectively passed at first and second edges of the input signal by using delayed signals.

[0021] The advantages of using an explicit pulse generator similar to the generator system 302 shown in FIG. 3 have been measured. For a target D-to-Q delay of 100 pico-seconds, the explicit-pulsed dual edge-triggered flip-flop element was measured to consume less energy than the single edge-triggered version. Additional energy savings may be realized in the clock distribution network.

[0022] While specific embodiments of the invention have been illustrated and described, other embodiments and variations are possible. For example, although the illustrated embodiments show the pulse generator being used in a flip-flop circuit, other circuits are envisioned that utilize the explicit pulse generator. Furthermore, the clock signal generated by the explicit pulse generator may be used for purposes other than for clocking. Thus, the pulse generator may be used in transition encoders for low-power busses, or in frequency doubler circuits.

[0023] All these are intended to be encompassed by the following claims. 

What is claimed is:
 1. A pulse generator system, comprising: a plurality of buffers to insert delays into an input signal, and generate a delay signal, said input signal having a series of pulses, each pulse having first and second edges; at least two transmission gates operatively coupled to said plurality of buffers, said at least two transmission gates including first and second transmission gates, where said first transmission gate selectively passes the input signal, and said second transmission gate selectively passes inverted signal of the input signal.
 2. The system of claim 1, wherein said first transmission gate selectively passes a first logic level on the first edge, and selectively passes a second logic level on the second edge after a delay, and said second transmission gate selectively passes the first logic level on the second edge, and selectively passes the second logic level on the first edge after a delay.
 3. The system of claim 2, wherein said first logic level is a logic low, and said second logic level is a logic high.
 4. The system of claim 2, wherein said first edge is a falling edge, and said second edge is a rising edge.
 5. The system of claim 1, wherein said delay signal controls first and second transmission gates to selectively pass portions of the input signal.
 6. The system of claim 1, wherein said plurality of buffers includes a plurality of inverters.
 7. The system of claim 6, wherein each of said first and second transmission gates includes an input terminal and an output terminal.
 8. The system of claim 7, wherein each of said first and second transmission gates further includes an NMOS transistor having gate, source, and drain terminals.
 9. The system of claim 8, wherein each of said first and second transmission gates further includes a PMOS transistor having gate, source, and drain terminals, where the source terminal of said NMOS transistor and the drain terminal of said PMOS transistor are commonly connected to said input terminal, and the drain terminal of said NMOS transistor and the source terminal of said PMOS transistor are commonly connected to said output terminal.
 10. The system of claim 9, wherein said plurality of inverters includes first, second, and third inverters, each of said first, second, and third inverters having an input node and an output node, said first, second, and third inverters connected in series, such that the output node of said first inverter is connected to the input node of said second inverter, and output node of said second inverter is connected to the input node of said third inverter.
 11. The system of claim 10, wherein the input node of said first inverter receives the input signal.
 12. The system of claim 11, wherein said input terminal of said first transmission gate receives the input signal.
 13. The system of claim 12, wherein said input terminal of said second transmission gate is coupled to the output node of said first inverter.
 14. The system of claim 13, wherein the NMOS gate terminal of the first transmission gate and the PMOS gate terminal of the second transmission gate are commonly coupled to the output of said second inverter.
 15. The system of claim 14, wherein the PMOS gate terminal of the first transmission gate and the NMOS gate terminal of the second transmission gate are commonly coupled to the output of said third inverter.
 16. The system of claim 15, wherein said output terminals of said first and second transmission gates are coupled together to provide an output signal having at least two pulses within one cycle of the input signal.
 17. A system, comprising: at least two inverters connected in series, each inverter to successively insert a delay into an input signal, and to generate a delay signal; at least first and second transmission gates coupled to said at least two inverters, and to each other, such that said first transmission gate selectively passes the input signal, and said second transmission gate selectively passes inverted signal of the input signal, where said delay signal controls said first and second transmission gates.
 18. The system of claim 17, wherein output terminals of said at least first and second transmission gates are coupled together to selectively pass said input signal, such that said at least first and second transmission gates produce an output signal having at least two pulses within one cycle of said input signal.
 19. The system of claim 17, wherein said at least two inverters include first, second, and third inverters.
 20. The system of claim 19, wherein said input signal is sent to said first transmission gate, and an output of said first inverter is sent to said second transmission gate.
 21. The system of claim 19, wherein outputs of said second and third inverters drive said first and second transmission gates, respectively.
 22. A method, comprising: successively inserting a delay into an input signal; coupling said input signal and delayed signals of the input signal; and using delayed signals to selectively pass the input signal at first and second edges of the input signal.
 23. The method of claim 22, wherein said selectively passing includes first passing a first logic level of the input signal responsive to the first edge of the input signal, and second passing a second logic level of the input signal responsive to the second edge of the input signal, after a delay.
 24. The method of claim 23, wherein said selectively passing further includes third passing a first logic level of the input signal responsive to the second edge of the input signal, and fourth passing a second logic level on the first edge of the input signal, after a delay.
 25. The method of claim 24, wherein said selectively passing further includes connecting outputs of said first, second, third, and fourth passings to selectively pass the input signal, such that said first, second, third, and fourth passings produce an output signal having at least two pulses within one cycle of the input signal.
 26. A flip-flop device, comprising: a buffer to save and output data; a first transmission gate to receive and selectively pass said data to said buffer; and a pulse generator to provide control signals for selection in said first transmission gate, said pulse generator including: at least two inverters connected in series, each inverter to successively insert a delay into an input signal, and to generate a delay signal, at least second and third transmission gates coupled to said at least two inverters, and to each other, said second transmission gate coupled to receive and selectively pass the input signal, and said third transmission gate coupled to receive and selectively pass inverted signal of the input signal, where said delay signal controls said first and second transmission gates.
 27. The device of claim 26, wherein output terminals of said at least second and third transmission gates are coupled together to selectively pass said input signal, said at least second and third transmission gates to produce an output signal having at least two pulses within one cycle of said input signal.
 28. The device of claim 27, further comprising: an inverter coupled to the output terminals of said second and third transmission gates, said inverter providing an inverted delayed signal of said output signal.
 29. The device of claim 28, wherein said output signal and said inverted delayed signal of said output signal controls selection in said first transmission gate. 